Synthesis of gold-decorated latexes via conducting polymer redox templates

The efficient electroless deposition of gold from aqueous solutions has bee n achieved via redox interaction between Au(III) ions and conducting polyme rs such polypyrrole, polyaniline and poly(3,4-ethylene-dioxythiophene). Whe n using the doped, conductive bulk powder forms of these polymers, the aver age size of the gold deposits decreased from ca. 10 to ca. 1 mum as the ini tial pH of the reaction solution was increased from pH 0 to 7. In experimen ts conducted at neutral pH, pH drift down to pH 3 occurred during the redox reaction. However, if the base-treated, non-conductive forms of the polyme rs were added to AuCl3 solutions at pH 7, the solution pH remained close to neutral, and finely dispersed gold deposits of 100-400 nm were obtained, s trongly suggesting that the gold nucleation is pH-dependent. These findings were then used in attempts to prepare gold-clad latex particles by using m icrometer-sized, conducting polymer-coated polystyrene latexes as redox tem plates for the reduction of gold from solution. Although it was not possibl e to obtain homogeneous gold coatings, a series of latex particles randomly decorated with 40-60 mn gold nanoparticles was obtained, with gold loading s of up to 12.5 wt% as measured by TGA. XPS studies confirmed the presence of metallic gold at the latex surface, in addition to an increase in the ox idation state of the conducting polymer overlayer, thus confirming that a r edox interaction had indeed occurred. Disk centrifuge studies clearly indic ated a marked decrease in the colloidal stability of the latexes after gold decoration. Finally, pressed pellet solid-state conductivity measurements showed the composite particles to be non-conductive, which is no doubt due to the discrete, well-sepa0rated nature of the gold nanoparticles on the la tex, which prevents efficient charge transport.